A fram tractor powered by a diesel engine exemplifies the conditions that call for the use of a torsional impulse damper. At any nominal speed of the diesel engine, the instantaneous speed of rotation of its crankshaft tends to fluctuate constantly, owing to events that occur during the engine cycle. If such speed variations are carried into the drive train, they produce vibration of the machine, may cause a certain amount of noise, and can subject the drive train to abrupt and constantly recurring high torsional loads that may damage its parts. A torsional impulse damper is therefore connected between the engine and the input shaft of the drive train, to smooth the torque variations of the engine.
In general, such a damper comprises a rotatable driving member connectable with the engine and a driven member that is coaxially rotatable with the driving member and is coaxially rotatable relative to it to a limited extent. Springs are so connected between the driving member and the driven member as to permit yielding relative rotation between them whereby the driving member is allowed to accelerate and decelerate with the engine and relative to the driven member, and these accelerations and decelerations are damped by friction means reacting between the driving member and the driven member.
In a typical prior torsional vibration damper installation, the driving member of the torsion damper had circumferential connections with the engine flywheel whereby it was constrained to coaxial rotation with the flywheel, while the driven member had a splined connection with an intermediate shaft that was confined to rotation on an axis coinciding with that of the flywheel. The intermediate shaft was supported at a front end thereof by a coaxial bearing in the flywheel, and its rear end portion projected through a flywheel housing in which there was a coaxial rear bearing for it. The rearmost portion of the intermediate shaft, which was outside the flywheel housing, had a universal joint connection with a drive shaft that extended rearwardly towards a driven mechanism.
It will be apparent that this arrangement was bulky, complicated and expensive. It required that the flywheel or the flywheel end of the crankshaft be provided with an accurately coaxial socket for the intermediate shaft front bearing; and to maintain the intermediate shaft coaxial with the flywheel, the flywheel housing that carried the rear bearing for the intermediate shaft had to project a substantial distance behind the flywheel and had to be rigid in itself and rigidly attached to the engine body.
There was no obvious way to reduce the cost, bulk and complexity of this prior construction because of the several requirements that must be met when a torsional impulse damper is connected between a flywheel and a universal joint drive shaft. One important requirement is that the front end of the universal joint shaft must have a connection that remains coaxial with the flywheel. The driving and driven members of the damper must be maintained in coaxial relation to one another as well as being free for limited rotation relative to one another. Another requirement is that any bearings in the system be well protected from dust and dirt. It is also highly desirable that the spring or springs of the damper as well as the friction sufaces of its driving and driven members be protectively enclosed. The flywheel should also be enclosed, and this implies that there should in any case be some type of housing for it. Thus each of the many parts of the above described prior mechanism served to meet one or more of these requirements, so that there seemed to be no satisfactory way of eliminating any of them.